Turkey Day!!!

Well, I'm about to leave for Thanksgiving week, and in a few minutes I'll be driving to the sprawling, gigantic Gallatin Field airport here in Bozeman (or should I say Belgrade). Anyway, it only has four gates, and can't service anything larger than a 737 (which it only does during the holidays).

I am super excited, mainly to see my family (who I haven't seen in several months), but also because of fieldwork - I have checked aerial photos, and there has been a LOT of coastal erosion, and it will only get worse (or in my case, better) between now and winter break.

You see, most paleontologists (here at MSU anyway) only get to their field areas in the summer, because its usually too damn cold to do so in the winter (although with a few Miocene land mammal spots around Bozeman, we've gone out in 20 degree weather before, and done jackets in 35 degree weather, with snow on the ground - we were really, really bored.... yeah...).

However, in California, it rarely dips below 45 degrees on the coast (and sometimes rarely above 55 in the winter), so it is possible to go out during this time of the year. However, in the winter, it is not only possible, it is usually far more productive as well. This is due to increased storm activity during the winter, and the increased chance of having cliff collapses (which really suck for the landowners above, who usually have pieces of their backyard now fifty feet lower, but is really good for me!). Also, during the summer the lack of extremely high tides and storms usually allows the cliffs to collect all sorts of dust, grime, and algae - storms during the winter usually clean off all this unsightly garbage, so that you can see clean, unweathered rock surfaces. I cannot begin to explain how much easier and more productive it makes collecting.

It also allows for the researcher to actually see sedimentary structures, and the detail of trace fossils (e.g. spreiten). Anyway, I have a good feeling about thanksgiving break, and a good feeling about winter break this year. Although I have no idea how I can top last winter break - a 40% complete fur seal skeleton (with partial skull), two partial odontocete skulls (one with partial skeleton, and a partial dentary), a 6" long Carcharocles megalodon tooth (aka bigass shark tooth), and a bunch of pinniped bones, bird bones, and shark teeth as icing on the cake.

I'll try to top that. I know I have at least one dolphin skull to excavate. Wish me luck, and Happy Thanksgiving!!!

Fun with volcanic tephra and invertebrates

One of the most useful sources of data with regards to dating a marine deposit are layers of volcanic ash or tephra. Often these can be dated directly, or chemically fingerprinted and matched to a parent body of igneous rock.

In the case of the Purisima Formation, some portions of it have more ash layers than others; Chuck Powell at the Menlo Park USGS tells me the section where this photo was taken has 13 different ash beds.

This ash bed in particular has been correlated with the Putah Tuff Member of the Tehama and Tuscan Formations of Northern California. The Putah Tuff is approximately 3.4 +/- 0.1 Ma, based on radiometric dating.

The problem with finding and utilizing tephra in the first place for dating or for tephrochronology of course is whether or not it gets preserved in the rock record. Ash forms before an eruption as bubbles form near the opening of a volcanic vent during the release of gas prior to an eruption; the magma that forms the material surrounding the gas cools and mineralizes. This mineralized material forming minute walls between gas bubbles then fragments as the eruption continues, and due to the small size (ash is classified by igneous petrologists and volcanologists as being >2mm) these fragments are then carried into the atmosphere via a 'current' of heated air before and during the eruption. Ash can stay in the atmosphere for long periods of time, and can even travel around the globe. Ash beds chemically identical to Yellowstone's Huckleberry Ridge Tuff (2.2 Ma) have been discovered in deep sea cores from the Northeastern Pacific Ocean. Since ash blows with the prevailing wind direction, and the prevailing winds in North America are westerlies, the ash apparently traveled around the earth (if anyone, e.g. Jeanette, has a reference for circumglobal ash deposition, let me know).

Typically, quieter ocean waters preserve ash better, as the ash needs to fall to the ocean surface, and settle to the sediment-water interface. High energy environments on the continental shelf rework sediment too rapidly to preserve discrete ash beds. However, there is also problem with depositing ash below storm- and fair-weather wave base: bioturbation.

Ah, those pesky critters geologists never like to pay much attention to - you know, animals. Well, in this case, geologists will probably like them even less. The problem is that below storm- and fair-weather wave base, bioturbation is insane - in some cases, like in the Purisima Formation, bioturbators effectively completely homogenize the sediment; I would estimate (based on ichnofabric index) that the sediments in these strata have bioturbated over 95% of the sediment, at least as preserved in a 6 km section of cliffs, which are 100-250' high; I'm too lazy to do the math, but that is a real shit load of sediment to churn through - and thats just in 2D - I don't even want to imagine what the actual volume of bioturbated sediment would be.

In the photograph I've posted (finally), you can see the Putah Tuff correlative ash bed. However, there's a twist - below the bed are the trace fossil Ophiomorpha nodosa, which invade sediments below the ash bed (Blue Arrow). These burrows are infilled with ash, and appear white on a brownish sandstone background. More Ophiomorpha nodosa invade the top of the ash bed, but are infilled with brownish sand(Red Arrow); again, there is beautiful contrast here with the brown filled burrows invading white ash.

In any event, those dastardly crustaceans weren't crafty enough to completely bioturbate the ash bed; the ash deposit was most likely too thick to be completely reworked. In all likelihood there is some sort of a preservational cutoff of ash thickness, although this would scale to the effectiveness of the bioturbating regime to homogenize sediment.

Fortunately, ichnofossils are extremely useful for paleoenvironmental reconstructions, so at least there is some information for geologists - not just a bunch of damn invertebrates destroying perfectly good sedimentary structures and ash layers.

P.s. I think I have a much better photo exemplifying this neat sand/ash contrast on a bioturbated contact; if I find it, I will post that as well).

Challenging Field Localities Part I

So, I'm going to start a series of posts on this site, which will be posted periodically. This post series will concentrate on challenging and technical fossil localities which I've dealt with - in the future, I might post about odd challenges others have faced in the field.

So, for the first post, I'll begin with more or less a conclusion/addition to the last post - how the hell my friend Tim got up there, why he went up there, and why I unfortunately followed.

The above photo is a mosaic of four or five pictures I took and later merged in photostitch. You can see a sort of a ramp on the left side, and a spot with some recognizable footprints. The spot with the footprints is the location of a 6-8" wide ledge, with an overhang underneath; at the time I weighed a few more pounds than Tim, even without any field gear besides my rock hammer (which I later tossed down to the beach so I didn't have to mess with it on my slow descent).

The second photo (at left) shows why we went up there in the first place - there is, in the upper right portion of the photo, a concave upward feature, which is about as long as Tim is tall (~6 feet). That is a mysticete whale mandible, and it is in a bonebed; pieces of bones from this bed had 'rained' down onto a 5' wide bench from this bonebed. To the right, the bed dips, and about 200' north intersects with the beach, and is accessible without a 20+' climb up a precarious, dusty, crumbling cliff. If I had my own rock climbing gear, it would be really awesome to rappel down to this bonebed.

Awesome fieldwork picture

Here is a gratuitous field photo I took three years ago; my friend Tim is about 25 feet above the beach or so. I just thought I should post this, as it is a rather awesome picture. I also used a small sliver of this picture for my personal webpage.

Don't worry, If I recruit you for a day trip in my field area, I won't put you through this. He went up there on his own. Maybe I'll post more on scary-ass fossil localities in the future. All these ideas!

Correction...

So, I totally forgot a very important part of the walrus anatomy, which my girlfriend reminded me...

But I'm not going to tell you. Its time for you to play 'which of these is not like the others...'

What's different?

AND, more importantly, does anyone out there (I.E. any of Annalisa's ex-students) have any suggestions on how to improve the reconstruction?

If noone does, then I'll assume my artwork is 100% perfect (as it usually is).

Reconstruction of a fossil walrus

At left is another reconstruction, this time of a fossil walrus, Valenictus chulavistensis. Valenictus chulavistensis was described by Tom Demere, the Paleontology Curator of the San Diego Natural History Museum.

Valenictus is a very odd pinniped, for several reasons. For one, V. chulavistensis (the only well known species of Valenictus) lacks all of its teeth, save the two elongate canines, which are fairly similar to the tusks of the extant walrus, Odobenus rosmarus. Nevertheless, modern walruses do not use their dentition for feeding, so while the disappearance of the noncanine dentition is unprecendented in other pinnipeds, it is not completely unsurprising as modern walrus noncanine teeth are nearly vestigial, so to speak.

Valenictus also has a number of postcranial features that are highly derived; the fore- and hind-limb bones do not closely resemble those of other fossil or modern Odobenidae (walruses). Also, the skeleton of Valenictus is pachyostotic and osteosclerotic (pachyostotic = thick bones, osteosclerotic = dense bones, more or less). This is possibly a ballast-like adaptation for maintaining bouyancy in a warm water environment.

These adaptations are also seen in sirenians. This is probably an adaptation for feeding in shallow, warm waters: the extant walrus feeds on benthic molluscs in shallow (but very, very cold) water, and (most) sirenians feed on seagrass in the photic zone. Valenictus chulavistensis evidently had many of the same feeding adaptations for molluscivory as does Odobenus, and Valenictus thus far has been found in relatively warm-watter settings, based on mollusc and microfossil assemblages. Additionally, other fossils of Valenictus are known from the proto-gulf of California (i.e. the Salton trough), which was hypersaline - this would have made a large, fat animal even more positively bouyant in the water column, a major hindrance to a critter that relies on benthic invertebrates as a food source.

I'll do some more in-depth posts on this fascinating fossil walrus in the future.

Extinct Mako tooth

Just a quick post, with a very pretty picture. Here is a fossil tooth of the "extinct" Bigtooth Mako shark, aka Isurus hastalis. This shark is the ancestor of the Great White Shark, Carcharodon carcharias. (Since Isurus hastalis and Carcharodon carcharias are simply Miocene and extant end members of an anagenetic lineage, Isurus hastalis didn't exactly go extinct, since it is more or less just a morphotype as opposed to a distinct species).

Later on I'll make up a post completely on the Isurus-Carcharodon transition in the Purisima Formation; there is now a fairly good sample size of teeth from the Isurus-Carcharodon lineage from the Purisima, that demonstrate the appearance of serrations and the increase in serration size through time. Oddly enough, you can see a bit of a little depression that the tooth sits in in the rock surface; that is the remains of a hole I dug for a partial fish skull exactly one year prior (spring break 07; this was 08).

This is one of the youngest occurrences of Isurus hastalis. Needless to say, I was pretty damn happy when I found this. Its a damn pretty tooth, and I'll be donating it to the SCMNH this winter break (If I haven't already - I can't recall).

Reconstruction of a fossil mysticete

At left is a skeletal reconstruction I recently did, which was supposed to go in my talk for SVP this year on a bizarre baleen whale named Herpetocetus bramblei. This skeletal reconstruction is based on a referred skeleton of Herpetocetus sendaicus from the early Pliocene of Japan.

Herpetocetus is a very weird type of baleen whale, and I will most likely be posting about some of its oddities in the future.

For example, there is a very odd 'style' of the suturing between the rostral elements (e.g. maxillae, premaxillae, nasals) and the posterior cranium (particularly the frontals). The mandible of this taxon is extremely strange, as is the jaw joint itself (e.g. glenoid fossa), and the auditory/temporal region of the cranium. The postcranial skeleton is, however, fairly normal for a cetacean.

Lastly, most species of Herpetocetus would have been in the ballpark of 4-5 meters in length, while H. bramblei, the largest known species, would have been in the 5-6 meter range. Still, in American, thats about 15-18 feet, for a large Herpetocetus. Most modern mysticetes occur in the 10 meter-plus range (again, 30 feet or more in American). There are a couple of smallish freaks, such as the Dwarf Minke Whale (an unnamed subspecies of Balaenoptera acutorostrata) and the Pygmy Right Whale (Caperea marginata), in the 6-8 meter and 4-6 meter range, respectively.

Another odd feature about fossil mysticetes is the tendency towards small size with respect to extant mysticetes. For one, this could be climatically controlled (large mysticetes are pretty much relegated to cold, nutrient rich waters much of the year). This also, however, could be sampling bias; several authors have suggested that because the majority of fossil mysticete crania are small (e.g. Herpetocetus), then fossil mysticetes probably were all that small (strongly paraphrased). However, the problem with this statement is that the skull of a 90 foot blue whale is over 12 feet long and 6+ feet wide; thats not exactly easy to excavate as a fossil, and not exactly easy to find complete, either.

Size in fossil cetaceans is worth a post all by itself; that'll come later.